This invention relates to apparatus for checking set-up errors by the operator of a machine tool, particularly but not exclusively a computer controlled machine tool.
Computer controlled machine tools, for example milling and routing machine tools, allow a reduction in the amount of supervision during machining, the operator merely having to set the machine tool up correctly, i.e. by fitting the correct cutter(s), setting the machine initially to the correct datum and so on, whereupon the machining can continue without further manual intervention. However, particularly in an industry such as the aircraft industry where the raw material costs of the workpiece to be machined may be very high indeed, the consequence of an error in setting-up, for example the selection of the wrong cutter or the wrong size of cutter, can be major.
Accordingly, there has been proposed a setting-aid for a computer controlled machine tool, which setting-aid comprises an anodised, approximately mushroom shaped "button" with a support device enabling the button to be fixed at a predetermined position on the worktable of a machine tool, the support device being such that the button is easily replaceable when necessary. Meanwhile, the program for any particular machining operation includes a check sequence which is carried out when the operator has set-up the machine tool and has indicated to the computer that it should begin the machining process. In this check sequence the tool, say an end-mill, of the machine tool is caused to move across the top surface of the button and to circle around it with a small, predetermined clearance. If an oversize cutter has been selected or the datum setting is too low, the cutter will contact the button during the check sequence, cut through the anodised surface thereof and produce an electrical fault signal.